Automatic choke mechanism



Jan. 25, 1966 E. L. NEMETZ 3,231,248

AUTOMATIC CHOKE MECHANISM Filed Sept. 17, 1962 5 Sheets-Sheet 1 0W4k0 A.IVEMETZ INVENTOR.

Jan. 25, 1966 E. L. NEMETZ 3,231,248

AUTOMATIC CHOKE MECHANISM Filed Sept. 17, 1962 5 Sheets-Sheet 2 501464004. A/[METZ INVENTOR ATTOR/VE VJ Jan. 25, 1966 E. L. NEMETZ 3,231,248

AUTOMATIC CHOKE MECHANISM Filed Sept. 17, 1962 3 Sheets-Sheet 5 0 waka4. A i H5712 I NVENTOR.

United States Patent 3,231,248 AUTOMATIC CHQKE MECHANISM Edward L.Nemetz, 02k Park, Mich, assignor to Ford Motor Company, Dearborn, Micln,a corporation of Delaware Filed Sept. 17, 1962, Ser. No. 223,997 5Claims. (Cl. 261-39) The present invention relates to automatic chokemechanisms for internal combustion engines.

Internal combustion gasoline engines such as are used in automobilesusually are provided with an automatic choke mechanism for automaticallychoking the engine for cold-weather starting and operation until theengine has become sufficiently warm for normal operation. Such automaticchokes conventionally are provided with a bimetallic, coiled spring,which, when cold, serves to close the choke valve on the carburetor,and, when heated, to open the valve. The bimetallic spring also servesto move a fast idle cam into operating position to limit closing of thethrottle valve at the carburetor when the en e is cold and cause theengine to run at a faster idle to prevent stalling. As the bimetallicspring becomes heated, it progressively rotates the fast idle cam out ofoperative position to provide less throttle opening at idle until,finally, the cam is rotated completely out of operative position, andclosing movement of the throttle is limited by the regular hot engineidle speed stop, thus producing the normal, slow idle of a warm engine.

According to the present invention, the action of the bimetallic springcontrolling the choke valve is modulated by a second spring which isenergized by return of the throttle to fast idle position, and whichtends to open the choke slightly at idle to prevent the engine fromrunning too rich, thus causing uneven engine idling and possiblestalling. The present invention also, by thus controlling the chokevalve, permits a desirable fast idle speed while the engine is coldwithout stalling of the engine, and also provides correct enrichment ofthe fuel-air mixture during driveaway.

Among the objects of the present invention are to provide an improvedautomatic choke mechanism in which the action of a bimetallic spring ismodulated by a second spring etfective as the throttle returns to idleposition to reduce choking of the engine at idle; to provide such amechanism in which the spring is engaged by the fast idle lever of thecarburetor as the throttle returns to idle position in order to exertforce on the bimetallic spring only at throttle positions one-third openor less; to provide an automatic choke which will choke more inaccordance with the requirements of an engine so as to preventcoldengine stalling; to provide such a mechanism in which the chokegives mixture enrichment during driveaway; and to provide a chokemechanism of simple, dependable operation.

Other objects, and objects relating to details and economics ofconstruction and use, will be apparent from the detailed description tofollow.

My invention is clearly defined in the appended claims. In the claims,as well as in the description, parts may at times be identified byspecific names for clarity and con venience, but such nomenclature is tobe understood as having the broadest meaning consistent with the contextand with the concept of my invention as distinguished from the pertinentprior art. The best form in which I have contemplated applying myinvention is illustrated in the accompanying drawings forming part ofthis specification, in which:

FIGURE 1 is a perspective view of a carburetor having a choke mechanismaccording to the present invention, the choke housing and associatedparts being separated from the rest of the mechanism for clarity ofillustration. The throttle is shown at starting position.

FIGURE 2 is a view similar to FIGURE 1, the throttle being shown at fastidle position.

FIGURE 3 is an exploded view of the choke control parts, the parts beingshown in the same general position as FIGURE 2.

Referring now to the drawings, the carburetor has a body 10 which isprovided with an air inlet 11. A choke valve or plate 12 is shaped toclose the inlet: 111., the plate being mounted on a shaft 14 extendingacross the air inlet and journaled Within the carburetor body It).Preferably, the choke valve is of unbalanced construction, having agreater area on one side of the shaft 14 than on the other so that thereduced pressure on the underside of the valve when in closed positiondue to air intake of the engine will tend to rotate the valve towardsopen position. A lever 15 is secured to an end of the choke 14.

A choke housing assembly 16 consists of a choke housing 17 secured tothe body of the carburetor. A choke housing shaft 19 is journaled withinthe assembly and is provided with a lever 20 fixed to the end of theshaft adjacent the body of the carburetor and connected with the lever15 by a link 21 so that rotation of the choke housing shaft opens andcloses the choke valve.

The choke housing shaft 19 has a lever 22 mounted on the shaft withinthe housing. The lever 22 is engaged by a bimetallic spring 24 havingspaced coils generally concentric with the shaft 19. The opposite end ofthe bimetallic spring is supported in a spring housing 25 which forms acover for the choke housing. The spring 24, when cold, biases the chokevalve 12 to closed position. The spring housing 25 is circular andclamped against the choke housing 17 by a generally circular clampingring 26 held in place by three screws 27 (only two shown in thedrawings). By slightly rotating the spring housing 25 on the chokehousing, the force with which the choke valve is biased closed may beadjusted.

Heated air is drawn from adjacent the exhaust manifold through theinterior of the choke housing 19 and into the intake manifold. Theheated air enters the choke housing through the air intake 29 and out ofthe housing through a passage 36, integral with a leg 31 of the chokehousing. Passage of the heated air through the housing serves to heatthe bimetallic spring 24, causing the spring to unwind as it becomesheated and thus bias the choke valve 12 to open position. A baflie 32,which may be mounted on the choke housing, prevents excessive chillingof the housing by flow of cold air passing over the engine, so as topermit the spring 24 to become heated at the proper rate.

Conventional throttle plates, not shown, are mounted in the lowerportion of the carburetor body by a transversely extending throttleshaft 34. The throttle shaft is operated by a lever and rod, not shown,on the opposite side of the carburetor. An engine idle speed adjustingscrew, not shown, adjacent the lever, limits closing movement of thethrottle shaft 34 in the customary manner to regulate idle speed of theengine when hot.

Idle speed of the engine when cold is regulated by a fast lever 35 fixedto the throttle shaft 34 and coacting with a fast idle cam as pivota-llymounted on a stud 37 projecting from the carburetor body a shortdistance above the throttle shaft. The fast idle cam 36 has a stepped,generally arcuate surface 39 engaged by a stop screw 49 mounted on thefast idle lever 35. Counterclockwise rotation of the cam 36 increasinglylimits return movement of the lever 35 and produces a faster idle, whileclockwise rotation of the cam reduce-s idle speed until the stop screw40 no longer contacts the cam and idle speed is regulated solely by thehot engine idle speed adg'ustment on the opposite side of thecarburetor.

The fast idle has a lever portion 41 projecting on the opposite side ofthe mounting stud 37 and connected with a bell crank 42 by a link 44.The bell crank 42 is provided with an arcuate slot 4-5 receiving thelink .4 to provide for limited indepenoent movement of the fast idle camand choke valve.

A torsion spring 46 is mounted on a spring carrier 47 pivotally receivedon the stud 3'7 beside the fast idle cam. The spring carrier 47 has atang engaged with one end of the spring 46. A second tang 51 of thecarrier is engaged with the other end 52 of the spring 4'! to maintainthe spring coiled about the carrier. A third tang 54, extending axiallyof the carrier 47, is engaged within an o ening 55' in the fast idlecam. A pin 56 extending axially from the fast idle lever engages theouter end portion of the end 52 of the Slilllg 46. An adjusting screw 57on the fast idle cam may be set against the upper side of the third tang54 of the spring carrier to adjust the point at which clockwise rotationof the carrier will pick up the fast idle cam and also rotate itclockwise.

The stiffness of the spring 2 5 is such that as the throttle returns tofast idle after a cold engine has been started, the pin 56 on the fastidle lever 35 will pick up the end 52 of the spring 46 and force thechoke open slightly against the bias of the bimetallic spring 24 toassure that the choke valve 12; is somewhat opened to prevent too muchchoking and an excessively rich idle mixture. As the bimetallic springbecomes heated and moves the choke towards open position, it will carrythe fast idle cam 36 clockwise so that the engine fast idling speed isreduced. The arcuate slot in the bell crank 42 functions in the usualmanner to permit movement of the choke valve under the counteractinginfluences of the bimetallic spring 24 and intake manifold vacuumwithout moving the fast idle cam.

In starting a cold engine having an automatic choke according to thepresent invention, the throttle plates should be moved to a position atleast one-third open by holding the accelerator pedal down. Thismovement of the throttle plates moves the pin of the fast idle cam awayfrom the end 52 of the torsion spring as, making the spring inoperativein opposing the bimetallic spring 24, and thereby making the full forceof the bimetallic spring available for completely closing the chokevalve 12 for easy starting in cold weather and permitting the bimetallicspring to select prope positioning of the choke valve for starting apartially warm engine.

In driveaway with a cold engine, as the throttle is moved from idleposition, the pin of the fast idle cam moves away from the end 52 of thetorsion spring 46. As above described in conn ction with cold enginestarting, the spring 24 is unopposed by the torsion spring 46 as soon asthe throttle is partially opened, which makes the full force of thebimetalli spring available for moving the choke valve 12. towards closedposition to enrich the mixture for acceleration.

As the bimetallic spring becomes heated during operation of the engine,it will move the choke valve towards open position. As soon as the Valvehas moved beyond the partially open starting position shown in FIGURES 2and 3, the torsion spring 46 will have no further affect on operation ofthe automatic choke I claim:

1. In an automatic choke assembly for a carburetor having an air inlet,a throttle valve, and a choke valve for closing the air inlet; abimetallic spring mounted on the carburetor and exposed to heat due toengine operation, linkage connecting the bimetallic spring with thechoke valve to bias it between open and closed position responsive totemperature of the spring, a fast idle cam pivotally mounted on thecarburetor for selectively limiting closing movement of the throttle,means linking the bimetallic spring to the fast idle cam to rotatebetween operative and non-operative positions responsive to temperatureof the bimetallic spring, means to resiliently bias tl e fast idle camtowards non-operative position against the bias of the bimetallicspring, and means to stress said biasing means upon return of thethrottle towards closed position so as to render said biasing meansoperative Only at idle and part-throttle operation, the bias of the fastidle cam overcoming the bias of the bimetallic spring and, actingthrough the linking means between the bimetallic spring and the fastidle cam, causing the choke valve to be opened slightly at cold engineidle.

2. in an automatic choke assembly for a carburetor having an air inlet,a th ottle valve, and a choke valve for closing the air inlet; abimetallic spring mounted on the carburetor and exposed to heat due toengine operation, linkage connecting the bimetallic spring with thechoke valve to bias it between open and closed position responsive totemperature of the spring, a fast idle Cam pivotally mounted on thecarburetor for selectively limiting closing movement of the throttle,means linking the bimetallic spring to the fast idle cam to rotate itbetween operative and non-operative positions responsive to temperatureof the bimetallic spring, means to resiliently bias the fast idle camtowards non-operative position against the bias of the bimetallicspring, and means to stress said biasing means upon return of thethrottle towards closed position so as to render said biasing meansoperative only at less than about one'third throttle opening, the biasof the fast idle cam overcoming the bias of the bimetallic spring and,acting through the linking means between the bimetallic spring and thefast idle cam, causing the choke valve to be opened slightly at coldengine idle.

3. In an automatic choke assembly for a carburetor having an air inlet,a throttle valve, and a choke valve for closing the air inlet; atc-mperature-sensitive spring mounted on the carburetor and exposed toheat due to engine operation, linkage connecting the temperatureperaturesensitive spring with the choke valve to bias it between open and closedpositions responsive to temperature of the spring, a fast idle campivotally mounted on the carburetor for selectively limiting closingmovement of the throttle, means linking the temperaturesensitive springto the fast idle cam to rotate it between operative and nonoperativepositions responsive to ternperat-ure of the temperature-sensitivespring, a torsion spring engaged with the fast idle cam and means tostress the torsion spring upon return of the throttle valve to wardsclosed position so as to render said biasing means operative only atidle and part-throttle operation for resiliently biasing the fast idlecam towards non-operative position against the bias of thetemperature-sensitive spring, the bias of the fast idle cam overcomingthe bias of the temperature sensitive spring and, acting through thelinking means between the temperatitre-sensitive spring and the fastidle cam, causing the choke valve to be opened slightly at cold engineidle.

In an automatic choke assembly for a carburetor having an air inlet, athrottle shaft, a throttle valve mounted on said shaft, and a chokevalve for closing the air inlet; a temperaturecensitive spring mountedon the carburetor and exposed to heat due to engine operation, linkageconnecting the temperature-sensitiye spring with the choke valve to biasit between open and closed positions responsive to temperature of thespring, a fast idle cam pivotally mounted on the carburetor forselectively limiting closing movement of the throttle, an arm fired tothe throttle shaft and engaging the fast idle cam to limit closingmovement of the throttle valve, means linking the temperature-semilivespring to the fast idle cam to rotate it between operative andnon-operative positions responsive to temperature of thetemperature-sensitive spring, and a torsion spring engaged with the fastidle cam and engaged and stressed by the arm upon return of the throttlevalve towards closed position for resiliently biasing the fast idle camtowards non-operative position against the bias of thetemperature-sensitive spring, the bias of the fast idle cam overcomingthe bias of the bimetallic spring and, acting through the linking meansbetween the bimetallic spring and the fast idle cam, causing the chokevalve to be opened slightly at cold engine idle.

5. In an automatic choke assembly for a carburetor having an air inlet,a throttle shaft, a throttle valve mounted on said shaft, and a chokevalve for closing the air inlet; a temperature-sensitive spring mountedon the carburetor and exposed to heat due to engine operation, linkageconnecting the temperature-sensitive spring with the choke valve to biasit between open and closed positions responsive to temperature of thespring, a fast idle cam pivotally mounted on the carburetor forselectively limiting closing movement of the throttle, an arm fixed tothe throttle shaft and engaging the fast idle cam to limit closingmovement of the throttle valve, means linking the temperature sensitivespring to the fast idle cam to rotate it between operative and nonoperative positions responsive to temperature of thetemperaturesensitive spring, and a torsion spring concentric with thepivotal mounting of the fast idle cam and engaged and stressed by thearm upon return of the throttle valve towards closed position forresiliently the fast idle cam towards non-operative position against thebias of the temperature-sensitive spring, the bias of the fast idle camovercoming the bias of the bimetallic spring and, acting through thelinking means between the bimetallic spring and the fast idle cam,causing the choke valve to be opened slightly at cold engine idle.

References Cited by the Examiner UNITED STATES PATENTS 2,124,778 7/1938Hunt 261-39 2,786,657 3/1957 Sutton 261-39 2,880,978 4/1959 Winkley261-39 2,998,233 8/1961 Marsee 261-39 3,085,792 4/1963 Hill 261-39 HARRYB. THORNTON, Primary Examiner. HERBERT L. MARTIN, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,231,248 January 25, 1966 Edward L Nemetz ror appears in the abovenumbered pat- It is hereby certified that er tters Patent should read asent requiring correction and that the said Le corrected below.

Column 4, line 40, strike out "perati lre"; column 6, line 4, after"resiliently" insert biasing Signed and sealed this 6th day of December1966.

( L) Attest:

ERNEST W. SWlDER Attesting Officer Commissioner of Patents EDWARD J.BRENNER-

1. IN AN AUTOMATIC CHOKE ASSEMBLY FOR A CARBURETOR HAVING AN AIR INLET,A THROTTLE VALVE, AND A CHOKE VALVE FOR CLOSING THE AIR INLET; ABIMETALLIC SPRING MOUNTED ON THE CARBURETOR AND EXPOSED TO HEAT DUE TOENGINE OPERATION, LINKAGE CONNECTING THE BIMETALLIC SPRING WITH THECHOKE VALVE TO BIAS IT BETWEEN OPEN AND CLOSED POSITION RESPONSIVE TOTEMPERATURE OF THE SPRING, A FAST IDLE CAM PIVOTALLY MOUNTED ON THECARBURETOR FOR SELECTIVELY LIMITING CLOSING MOVEMENT OF THE THROTTLE,MEANS LINKING THE BIMETALLIC SPRING TO THE FAST IDLE CAM TO ROTATE ITBETWEEN OPERATIVE AND NON-OPERATIVE POSITIONS RESPONSIVE TO TEMPERATUREOF THE BIMETALLIC SPRING, MEANS TO RESILIENTLY BIAS THE FAST IDLE CAMTOWARDS NON-OPERATIVE POSITION AGAINST THE BIAS OF THE BIMETALLICSPRING, AND MEANS TO STRESS SAID BIASING MEANS UPON RETURN OF THETHROTTLE TOWRDS CLOSED POSITION SO AS TO RENDER SAID BIASING MEANSOPERATIVE ONLY AT IDLE AND PART-THROTTLE OPERATION, THE BIAS OF THE FASTIDLE CAM OVERCOMING THE BIAS OF THE BIMETALLIC SPRING AND, ACTINGTHROUGH THE LINKING MEANS BETWEEN THE BIMETALLIC SPRING AND THE FASTIDLE CAM, CAUSING THE CHOKE VALVE TO BE OPENED SLIGHTLY AT COLD ENGINEIDLE.